You can use IDL's FILESEARCH.  For example: files = FILE_SEARCH(*.dat', count=count)

Thank you so much a great help. Idl can do anyting

Another trick you could use is the spawn function which will place all the filenames into a text file. For example the following command spawn, 'dir/B/S E:\01.01\* > c:\filesXX.txt' Creates a text file called filesXX in the C drive, which contains the names of all files in the folder E:\01.01\.  One caveat is that it becomes more difficult if the folder you are interested in contains spaces in it's name (e.g. if it is in Documents and settings) as spawn doesn't like it.